1. Field of the Invention
The present invention relates generally to multi-channel systems, and more particularly to code-division multiplexed multi-channel systems.
2. Background Information
A multitude of applications require a front-end integrated circuit to manage multiple signals measured from different inputs. Examples of such multi-channel systems include: microelectrode arrays in neural recording, multi-antenna wireless communications, microarrays and lab-on-chips, X-ray detectors, electronic noses and gas sensor arrays, biosensor arrays, tactile sensors, ultrasound, cantilever arrays, multi-electrode electrocardiogram (ECG), and more. Even a generic architecture where multiple sensor outputs are processed by a single integrated circuit in industrial and medical applications falls under the category of a multi-channel system. Moreover, the emerging trend of miniature sensor arrays, which micro-electro-mechanical systems (MEMS) technology has enabled, is fueling the growing importance of low power, small form factor multi-channel integrated circuits.
A challenge of a multi-channel integrated circuit involves managing multiple input channels (which in some applications may range up to hundreds or even thousands of channels), while at the same time achieving reasonable amounts of power consumption and hardware size and complexity. In its most generic form, the multi-channel integrated circuit takes on the conventional architecture of FIG. 1, where multiple analog signal processing chains are dedicated to each input. However, several drawbacks accompany the brute-force replicated chain method: an increase in power consumption and chip area proportional to the number of inputs, an increase in I/O and control signals, coupling between multiple chains, difficulty in routing and distributing clock and global signals, and (non)systematic mismatches between the chains. Particularly, a critical bottleneck in multi-channel systems is the analog-to-digital converter (ADC), which, depending on the application, can easily dominate the overall power and area, especially when high resolutions and fast sampling speeds are needed. Consequently, not only does the conventional architecture increase design and debugging time, but in applications where ultra low power consumption and small chip area are the foremost goals, the architecture is prohibitively challenging
One alternative is to time-division multiplex (TDM) multiple input signals to a single shared path of an amplifier and analog-to-digital converter (ADC) as shown in FIG. 2. Another alternative is code-division multiplexing (CDM).